Does SM have the best discography?

[RVBPTLN]

Yes, unless you prefer hip hop. 

For pop/kpop, they have the best and deepest discography. 

They've had some of the most successful groups of all time in large part due to this.

HOT, SES, Shinwha, Boa, DBSK, Suju, SNSD, Shinee, Fx, Exo, RV

Their title tracks can be hit and miss because they like to experiment, but their albums always have great b-sides as well.